1 {-# OPTIONS -XRankNTypes -XMultiParamTypeClasses -XNoMonomorphismRestriction -XTypeOperators -XFunctionalDependencies #-}
2 -----------------------------------------------------------------------------
4 -- Module : GHC.HetMet.GArrow
6 -- License : public domain
8 -- Maintainer : Adam Megacz <megacz@acm.org>
9 -- Stability : experimental
10 -- Portability : portable
12 module GHC.HetMet.GArrow (
22 GArrowLiteral(..), -- should be implemented, but never invoked, by user code
24 GArrowSum(..), ga_inl, ga_inr,
38 import Control.Category
40 ------------------------------------------------------------------------
41 -- The main GArrow class
43 class Category g => GArrow g (**) u | (**) -> u, u -> (**) where
45 --comp :: g x y -> g y z -> g x z
46 ga_first :: g x y -> g (x ** z) (y ** z)
47 ga_second :: g x y -> g (z ** x) (z ** y)
48 ga_cancell :: g (u**x) x
49 ga_cancelr :: g (x**u) x
50 ga_uncancell :: g x (u**x)
51 ga_uncancelr :: g x (x**u)
52 ga_assoc :: g ((x** y)**z ) ( x**(y **z))
53 ga_unassoc :: g ( x**(y **z)) ((x** y)**z )
56 ------------------------------------------------------------------------
57 -- The three context-manipulation classes
59 class GArrow g (**) u => GArrowCopy g (**) u where
62 class GArrow g (**) u => GArrowDrop g (**) u where
65 class GArrow g (**) u => GArrowSwap g (**) u where
66 ga_swap :: g (x**y) (y**x)
69 ga_swap >>> ga_first f >>> ga_swap
70 -- implementation of ga_second for GArrowSwap
72 -- http://haskell.org/haskellwiki/Class_system_extension_proposal
73 -- "Allowing superclass methods to be overridden in derived classes";
74 -- if we had this we could do a better job here
78 ------------------------------------------------------------------------
79 -- Products, Coproducts, etc
82 class (GArrow g (**) u,
84 GArrowProd g (**) u (<*>) v
86 -- fundep: in any given context, (<*>) may serve as the
87 -- product for at most one GArrow
89 (<*>) -> v, v -> (<*>) where
90 ga_prod_copy :: g x (x<*>x)
93 class (GArrow g (**) u,
95 GArrowSum g (**) u (<+>) v
97 -- fundep: in any given context, (<+>) may serve as the
98 -- coproduct for at most one GArrow
100 (<+>) -> v, v -> (<+>) where
101 ga_merge :: g (x<+>x) x
104 -- Note to self: do not remove this type declaration; it ensures that if
105 -- I fiddle with the GArrowSum fundeps and get them wrong (i.e. insufficient)
106 -- I'll find out about it when compiling the base library.
107 ga_inl :: GArrowSum g (**) u (<+>) v => g x (x<+>y)
108 ga_inl = ga_uncancelr >>> ga_second ga_never
110 ga_inr :: GArrowSum g (**) u (<+>) v => g x (y<+>x)
111 ga_inr = ga_uncancell >>> ga_first ga_never
114 ------------------------------------------------------------------------
117 class GArrow g (**) u => GArrowLoop g (**) u where
118 ga_loopl :: g (x**z) (y**z) -> g x y
119 ga_loopr :: g (z**x) (z**y) -> g x y
122 ------------------------------------------------------------------------
123 -- Literal. Note that ga_literal should never appear in (unflattened)
124 -- Haskell programs, though the user may wish to write implementations
125 -- of this function (I haven't yet found a way to enforce this
126 -- restriction using exports)
128 class GArrow g (**) u => GArrowLiteral g (**) u t r where
129 ga_literal :: t -> g u r
134 ------------------------------------------------------------------------
135 -- Constant and Run, which are dual to each other
137 class GArrow g (**) u => GArrowEval g (**) u r t where
138 ga_eval :: g u r -> t
140 class GArrow g (**) u => GArrowConstant g (**) u t r where
141 ga_constant :: t -> g u r
145 ------------------------------------------------------------------------
146 -- Reify and Reflect, which are "curried" versions
148 -- If you have this for R the identity map on types, you're basically
149 -- a Control.Arrow; you can also define essentially all the other
150 -- methods of GArrow, GArrowDrop, GArrowCopy, etc in terms of this.
151 class GArrow g (**) u => GArrowReify g (**) u x y r q where
152 ga_reify :: (x -> y) -> g r q
154 class GArrow g (**) u => GArrowReflect g (**) u r q x y where
155 ga_reflect :: g r q -> (x -> y)
160 ------------------------------------------------------------------------
163 class GArrow g (**) u => GArrowApply g (**) u (~>) where
164 ga_applyl :: g (x**(x~>y) ) y
165 ga_applyr :: g ( (x~>y)**x) y
167 class GArrow g (**) u => GArrowCurry g (**) u (~>) where
168 ga_curryl :: g (x**y) z -> g x (y~>z)
169 ga_curryr :: g (x**y) z -> g y (x~>z)
174 ------------------------------------------------------------------------
175 -- Commonly Implemented Collections of Classes
178 -- The simply typed KAPPA calculus; see Hasegawa, __Decomposing Typed
179 -- Lambda Calculus into a Couple of Categorical Programming
180 -- Languages__, http://dx.doi.org/10.1007/3-540-60164-3_28
182 class (GArrowDrop g (**) u,
184 GArrowSwap g (**) u) =>
187 -- The simply typed LAMBDA calculus
188 class (GArrowSTKC g (**) u,
189 GArrowCurry g (**) u (~>),
190 GArrowApply g (**) u (~>)) =>
191 GArrowSTLC g (**) u (~>)
193 -- Programming Language for Computable Functions (w/o integers and booleans)
194 class (GArrowSTLC g (**) u (~>),
195 GArrowLoop g (**) u) =>
196 GArrowPCF g (**) u (~>)